Nowadays the execution of determined operations, such as for example painting, cleaning and assembly, or the execution of various different forms of processing, such as for example those for the removal of shavings, require the piece and/or blank to be locked in a specific position for the processing thereof.
In the field of processing for the removal of shavings, the use is undoubtedly known of machine tools such as, for example, lathes, milling machines, drills and grinding machines.
These machines are usually used in environments which are distinguished by production runs of many and varied products or blanks in small batches.
In many situations the use of such machine tools is essential in workshops which produce individual pieces, made to order.
It follows from this that there is the necessity to organise a production system that is particularly versatile, i.e. which can be adapted to the manufacture of several and heterogeneous products, made usually as unique pieces, or in an extremely limited run, in the majority of cases.
This type of system, commonly called Job-Shop, practically represents the stereotype of the production method which is the exact opposite of that which characterises mass production.
Mass production consists in the manufacture of a small quantity of different types of product, each of which is however reproduced on a large scale in huge quantities, which can vary between the thousands or even millions of batches.
While in mass production it is normal to automate the production process by means of a suitable layout of dedicated machines which are mutually connected in sequence, the same can not be said for production to order.
In production to order, the necessity to make use of a production system that is flexible, i.e. a system which can potentially be adapted to the implementation of several types of production, precludes the possibility of entirely automating the production by means of organising the system that is adapted to obtain a single type of product.
In production to order, the lack of an absolute automation thus confers importance upon manual interventions.
In particular, it is appropriate to note that the positioning and associated fixing of the piece to be worked on onto the machine tool are carried out manually.
Vice versa, in mass production, these same preliminary operations are carried out automatically by robots or mechanical anthropomorphic arms with varying degrees of freedom.
In using the machine tools normally adopted in a Job-Shop system, the use is widely known of vices, or some form of manual devices adapted to permit the positioning and subsequent locking in place of the piece to be worked on with the machine tool.
The use of such locking devices of known type is in any case also widespread in working environments which are entirely different from the above mentioned environment, for example in order to be able to carry out painting or cleaning operations, or the assembly of two or more bodies.
More generally, such devices of the known type are indispensable whenever the stable locking in place is required of an object to be worked on, by means of generic operations which are also simple, not necessarily concerning a purely industrial environment.
The devices of known type are usually constituted by a pair of vertical spacer elements, the height of which and the relative distance of which can be varied as a function of the dimensions and of the shape of the piece to be locked in place.
Such spacer elements have, in an upper region, means of interconnection for a pair of substantially horizontal supports or arms, arranged in mirror-symmetry with respect to each other and brought into engagement with the piece to be locked in place at the lower surfaces thereof.
Each support has, substantially centrally, a hole that is adapted to permit the passage of a vertical rod, which is substantially parallel to the corresponding spacer element, and is coupled underneath to the work bench of the machine tool.
Such rod has in an upper region a threaded end which protrudes from the support, so as to permit the removable interconnection of means adapted to the temporary fixing of such rod, such as, for example, counter-threaded nuts.
The piece to be worked on, which usually has a substantially squared shape, can then be preliminarily interposed between the pair of supports arranged mirror-symmetrically with respect to each other.
Subsequently the adjustment of the supports is carried out, both of their height and of their relative distance, as a function of the dimensions of the piece interposed between them.
The operation to lock the piece in place is then performed by means of the contact under pressure expressed between an end portion of the lower surface of the supports and two opposite ends of the upper surface of such piece.
A significant drawback, found in devices of the known type, lies precisely in the fact that in order to achieve a stable locking in place of the piece it is necessary to bring both of the spacer elements of the locking device into contact with two opposite lateral faces of such piece.
This precludes the possibility of working on these lateral faces, which, since they are affected by such approaching, do not have surfaces which are free so as to permit contact with the tool or, more generally, with the component of any machine tool.
Following from this is the necessity of having to subsequently remove the piece and positioning it according to a new orientation such as to permit the exposure of the two lateral surfaces which before were partially concealed by the locking elements.
A further aggravating circumstance of the above mentioned problem consists in the fact that, when the piece is locked in place, it has at least three surfaces upon which no work can be performed, the third surface, in addition to the lateral surfaces adjacent to the locking elements, being the lower surface, which is resting entirely on the workbench of the machine tool.
Following from this is the necessity of having to resort to multiple subsequent positioning operations and associated locking operations of the piece, with the further aggravating circumstance of repeatedly make systematic errors of positioning, which will thus have negative repercussions for the overall precision that can be achieved at the end of working on the piece.
Another drawback noted in such devices of the known type lies in the necessity of availing of qualified labour in order to be able to carry out the delicate preliminary operations of positioning and centering the piece.
A further drawback, which often occurs in such locking devices of the known type, consists in the possible damaging of the piece owing to localised deformation, at the surfaces which have already been worked on and are subsequently subjected to contact with the supports, in order to permit the operator to work on any surfaces of the piece that have not yet been worked on.
A significant problem, in addition to the problems already cited, refers to the considerable expenditure of time caused by repeated successive releasing, repositioning and re-locking operations on the piece which is destined for any form of processing on more than one surface.
In order to overcome the above mentioned drawbacks, a fixing system has been developed which can be interposed between the blank to be worked on and a work plate fixed to the reference system of the machine with which to carry out the work, which substantially comprises a plurality of fixing elements which are constituted by two opposing portions each provided with jaws which are adapted to engage, respectively, with two threaded pins which can be screwed in respective threaded holes which are formed both on the work plate and on the blank.
Moreover, a variation of the above mentioned system is known which consists in the fact that it comprises a device for gripping the blank in place of the threaded pin which can be associated with the blank and, more precisely, in the hole in which one of the threaded pins would be screwed.
Such other fixing systems of known types are not free from drawbacks, including the fact that, since the work plate has a pitch of the threaded seats that is almost constant, it is not always possible to stably fix the blank because the seats of the work plate may not correspond to the threaded or non-threaded holes of the blank with which to associate the fixing element.